Yan et al. used CRISPR/Cas9 to insert a large CAG repeat (150 CAGs) into the endogenous pig HTT gene in fibroblast cells and employed the SCNT to generate a HD KI pig model expressing full-length mutant HTT at the endogenous level (Yan et al., 2018), whose brains presented severe and preferential neurodegeneration in the medium spiny neurons like HD patients. The gene discussed is HTT; the disease is Huntington disease.